1. Technical Field
The present disclosure relates to a display device with a touch detection function which enables an external proximity object to be detected based on a change in capacitance and to an electronic apparatus including the same.
2. Description of the Related Art
In recent years, attention has been focused on a display device with a touch detection function which has a touch detection device that is touch panel provided on a display device such as a liquid crystal display device or which has a touch panel and a display device integrated with each other. Various types of button images are displayed on the display device, thereby enabling the entry of information in place of typical mechanical buttons. The display device having such a touch panel requires no input device like the keyboard, mouse, or key pads, and thus has been extensively used, for example, with portable information device like mobile telephones as well as computers.
Although there exist several touch detection schemes such as the optical type and the resistive type, the mobile device, in particular, tends to employ a capacitive type which provides a relatively simple structure and requires low power consumption. The capacitive touch detection device is provided with capacitance between drive electrodes, to which a drive signal is applied, and touch detection electrodes so as to detect a change in capacitance caused by an external object being brought into contact with or proximity to the device, that is, a change in voltage waveform that appears on the touch detection electrodes, thereby determining whether or not there is a touch.
With the touch detection device, there is a possibility that noises resulting from disturbance (disturbance noises) may propagate to the touch detection electrodes to cause a malfunction of the touch panel in the touch detection operation. FIG. 35 is an explanatory view illustrating the relationship between the frequency of a touch detection drive signal and a disturbance noise. For example, with a drive signal of 250 [kHz] being applied to the drive electrodes, there is a possibility of causing a malfunction when the disturbance noise having a high level at around 250 [kHz] as illustrated in FIG. 35, that is, the disturbance noise having a disturbance noise peak 101 is propagated to the touch detection electrodes. More specifically, there may occur a malfunction of the touch detection operation, in the case of which a change in voltage waveform appearing on the touch detection electrodes due to the disturbance noise may be determined to be a change caused by an external object being brought into contact with or proximity to the device. That is, it may be possibly determined that the external object has been brought into contact with or proximity to the device even when no external object has been actually brought into contact with or proximity to the device.
In order to address this problem, for example, Japanese Patent Application Laid-open Publication No. 2010-015262 discloses a capacitive touch detection device which detects the level of a disturbance noise and avoids a frequency in the vicinity of the frequency of the disturbance noise, thereby preventing a malfunction of the touch detection operation resulting from the disturbance noise. For example, as illustrated in FIG. 35, the occurrence of malfunction is prevented by changing the frequency of the drive signal from 250 [kHz] to a selected drive frequency 102.
To control the touch detection operation depending on the component of disturbance noise, the component of the disturbance noise has to be detected. Japanese Translation of PCT Patent Application Laid-open Publication No. 2012-503831 suggests that there should be provided a noise measurement period for detecting a disturbance noise in addition to the touch detection period.
The display device with a touch detection function may be conceivably configured such that the noise measurement period for detecting a disturbance noise is set to a period other than the display operation period in which the liquid crystal display device performs a write operation to write an image and the touch detection period in which the touch detection device performs a touch detection operation to detect whether an external object has been brought into contact with or proximity to the touch panel. In this case, the display device with a touch detection function measures a disturbance noise in a noise measurement period and then based on the measurement result, determines the drive frequency of touch detections, and alternately executes the display operation period and the touch detection period a certain number of times. After executing the display operation period and the touch detection period a certain number of times, the display device with a touch detection function measures the disturbance noise in the noise measurement period.
When the display operation period, the touch detection period, and the noise measurement period are provided in a time divisional manner, there will be an increase in the length of time in which neither the display operation period nor the touch detection period is executed in one frame, thus causing a decrease in the time to be assigned to the display operation period and the touch detection period. A decrease in time of the display operation period and the touch detection period would make it difficult to improve the display performance and the touch detection performance.
For the foregoing reasons, there is a need for a display device with a touch detection function which can improve the display performance and the touch detection performance and an electronic apparatus which includes the same.